Multi-tiered telescope shaped atomizer

ABSTRACT

In one example, a system is provided, comprising an exhaust reductant injector upstream of a mixer. The mixer includes a plurality of concentrically smaller rings interconnected via fins having a width varying in a flow direction, the fins arranged annularly, and with a first set of fins between a first pair of adjacent rings angularly offset from a second set of fins between a second pair of adjacent rings, the first and second pairs of rings sharing one common ring. In this way, it is possible to atomize, redirect, and mix the exhaust flow over a short distance to effectively react with NOx in a downstream SCR catalyst.

BACKGROUND

A technology such as Selective Catalyst Reduction (SCR) may be utilizedfor NOx reduction and to achieve diesel emissions requirements. In oneapproach, aqueous urea is sprayed into the exhaust gas stream whichsubsequently reacts with NOx on the surface of an SCR catalyst,resulting in reduction of engine-out NOx emissions. For improved NOxreduction under some conditions, the liquid urea sprayed into the dieselexhaust is typically atomized and mixed before it reaches the catalystsubstrate.

In one mixing approach, a two-mixer system may be utilized to providesuch mixing, where a first element (e.g., an atomizer) of the systemredirects the exhaust flow and catches the urea spray for atomization,and a second element (e.g., a twist mixer) aids in mixing the exhaustflow. As an example, the atomizer may include several (e.g., nine)louvers, and the twist mixer may include a helical mixing element whichis welded onto a center rod.

The inventors of the present application have recognized a problem insuch previous solutions. For example, twisting the flow requires acertain length, or distance, in order to impart sufficient angularmomentum to the flow, without overly restricting the flow and creatingtoo much back-pressure. However, some vehicle configurations mayrestrict available packaging space, particularly the length between thereductant injection and the position of the SCR catalyst.

SUMMARY

In one example, the above issues may be at least partially addressed bya system, comprising: an exhaust reductant injector upstream of a mixerincluding: a plurality of concentrically smaller rings interconnectedvia fins having a width varying in a flow direction, the fins arrangedannularly, and with a first set of fins between a first pair of adjacentrings angularly offset from a second set of fins between a second pairof adjacent rings, the first and second pairs of rings sharing onecommon ring. The geometry created by this structure can be used to drawsurrounding flow around and through the fins, thus improving mixing andvaporization of injected liquid reductant impacting the fins.

It should be understood that the summary above is provided to introducein simplified form a selection of concepts that are further described inthe detailed description. It is not meant to identify key or essentialfeatures of the claimed subject matter, the scope of which is defineduniquely by the claims that follow the detailed description.Furthermore, the claimed subject matter is not limited toimplementations that solve any disadvantages noted above or in any partof this disclosure.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 illustrates an exhaust system for receiving engine exhaust gas.

FIG. 2 illustrates a face-on view of an exhaust system atomizer drawnapproximately to scale in accordance with an embodiment of the presentdisclosure.

FIG. 2A illustrates a portion of the exhaust system atomizer of FIG. 2.

FIG. 3 illustrates a side view of the exhaust system atomizer of FIG. 2drawn approximately to scale.

FIG. 3A illustrates a portion of the exhaust system atomizer of FIG. 2.

FIG. 4 illustrates an isometric view of the exhaust system atomizer ofFIG. 2 drawn approximately to scale.

FIG. 4A illustrates a portion of the exhaust system atomizer of FIG. 2.

FIG. 5 illustrates a face-on view of an exhaust system atomizer drawnapproximately to scale in accordance with another embodiment of thepresent disclosure.

FIG. 5A illustrates a portion of the exhaust system atomizer of FIG. 5.

FIG. 6 illustrates an isometric view of the exhaust system atomizer ofFIG. 5 drawn approximately to scale.

FIG. 6A illustrates a portion of the exhaust system atomizer of FIG. 5.

FIG. 7 illustrates a side view of the exhaust system atomizer of FIG. 5drawn approximately to scale.

FIG. 7A illustrates a portion of the exhaust system atomizer of FIG. 5.

FIG. 8 illustrates an isometric view of an exhaust system atomizer drawnapproximately to scale in accordance with still another embodiment ofthe present disclosure.

FIG. 8A illustrates a portion of the exhaust system atomizer of FIG. 8.

FIG. 9 illustrates an isometric view of an exhaust system atomizer drawnapproximately to scale in accordance with yet another embodiment of thepresent disclosure.

FIG. 9A illustrates a portion of the exhaust system atomizer of FIG. 9.

DETAILED DESCRIPTION

A multi-tiered telescope-shaped exhaust system atomizer is disclosed.The exhaust system atomizer comprises a plurality of ringsinterconnected via fins, the rings and fins arranged concentricallyabout a common central axis. Ring diameters may decrease as the exhaustsystem atomizer is traversed in the direction of exhaust flow, while thefins orient towards the common central axis. Such an exhaust systematomizer may be appropriate for parabolic exhaust flow, and may reduceexhaust system weight and cost, as well as packaging space. However,other applications are also possible, and various modifications andalternative embodiments may be used, if desired.

FIG. 1 illustrates an exhaust system 100 for transporting exhaust gasesproduced by an internal combustion engine 110. As one non-limitingexample, engine 110 includes a diesel engine that produces a mechanicaloutput by combusting a mixture of air and diesel fuel. Alternatively,engine 110 may include other types of engines such as gasoline burningengines, among others.

Exhaust system 100 may include one or more of the following: an exhaustmanifold 120 for receiving exhaust gases produced by one or morecylinders of engine 110, a mixing region 130 arranged downstream ofexhaust manifold 120 for receiving a liquid reductant, a selectivecatalytic reductant (SCR) catalyst 140 arranged downstream of the mixingregion 130, and a noise suppression device 150 arranged downstream ofcatalyst 140. Additionally, exhaust system 100 may include a pluralityof exhaust pipes or passages for fluidically coupling the variousexhaust system components. For example, as illustrated by FIG. 1,exhaust manifold 120 may be fluidically coupled to mixing region 130 byone or more of exhaust passages 162 and 164. Catalyst 140 may befluidically coupled to noise suppression device 150 by exhaust passage166. Finally, exhaust gases may be permitted to flow from noisesuppression device 150 to the surrounding environment via exhaustpassage 168. Note that while not illustrated by FIG. 1, exhaust system100 may include a particulate filter and/or diesel oxidation catalystarranged upstream or downstream of catalyst 140. Furthermore, it shouldbe appreciated that exhaust system 100 may include two or morecatalysts.

In some embodiments, mixing region 130 may include a greatercross-sectional area or flow area than upstream exhaust passage 164.Mixing region 130 may include an injector 136 for selectively injectinga liquid into the exhaust system. As shown in FIG. 1, injector 136 maybe angled to inject liquid obliquely toward the mixer. Alternatively,injector 136 may be positioned in-line with the mixer to inject liquidalong the direction of exhaust flow. In one non-limiting example, theliquid injected by injector 136 may include a liquid reductant 178 suchas ammonia or urea. The liquid reductant 178 may be supplied to injector136 through conduit 174 from a storage tank 176 via an intermediate pump172. Mixing region 130 may also include an exhaust system atomizer 200,as described in further detail with regard to FIGS. 2-9. Note thatcatalyst 140 can include any suitable catalyst for reducing NOx or otherproducts of combustion resulting from the combustion of fuel by engine110.

With regards to vehicle applications, exhaust system 100 may be arrangedon the underside of the vehicle chassis. Additionally, it will beappreciated that the exhaust passage may include one or more bends orcurves to accommodate a particular vehicle arrangement. Further still,it will be appreciated that in some embodiments, exhaust system 100 mayinclude additional components not illustrated in FIG. 1 and/or may omitcomponents described herein.

FIGS. 2-9 illustrate various additional details of a portion of theexhaust passage for receiving engine exhaust gas, including exhaustsystem atomizers 200, 300, and 400, and 500, each of which may belocated inside mixing region 130. For example, each of the exhaustsystem atomizers may be positioned internally to (e.g., press-fit into)an exhaust pipe (e.g., exhaust passage 164 in FIG. 1) of engine 110 suchthat its outer edge is contiguous and in face-sharing contact with aninner wall 203 of mixing region 130, as seen in FIG. 3.

FIG. 2 shows a face-on view of an example embodiment of an exhaustsystem atomizer 200, which may also be referred to as a mixer. Theatomizer 200 comprises an array of circular rings 202, 206, 208 and 228,positioned in a telescope-shaped configuration with diameters decreasingin a flow direction. A first ring 202 is arranged at a furthermostupstream position, and defines an interior passage inlet 204 configuredto receive engine exhaust gas. Downstream of first ring 202 is provideda second ring 206, having a diameter less than that of first ring 202.Further downstream of second ring 206 is provided a third ring 208having a diameter less than that of first and second rings 202 and 206.Finally, a fourth ring 228, having a diameter less than that of rings202, 206 and 208, is provided at a furthermost downstream position, anddefines an interior passage outlet 211. Rings 202, 206, 208 and 228 intotality are arranged directly downstream one another, share a portionof an interior passage defined by inlet 204 and outlet 211, and arealigned concentrically about a common central axis 205. Thus, in such anexample, all rings are concentric to one another. Central axis 205 maybe concentric with the central axis of the exhaust pipe (e.g., exhaustpassage 164 in FIG. 1), such that a central axis of each ring andcentral axis 205 aligns with the central axis of the exhaust pipe.

The array of concentric rings (e.g., 202, 206, 208 and 228 in FIG. 2)may share a variety of common attributes. One non-limiting example mayinclude thickness, wherein thickness is a measurement of length alongcentral axis 205. As they are arranged progressively downstream in thedirection of exhaust flow, ring diameters may be reduced by a constantfactor; e.g., the diameter of the third ring 208 arranged concentricallydownstream the second ring 206 may be 20% less than that of the secondring 206, while the diameter of the second ring 206 may also be 20% lessthan that of the first ring 202, and so on. However, it will beappreciated that this is a non-limiting example and that diameterdifferences may vary among ring pairs or by a number of differentfactors.

The atomizer of the present disclosure may be formed integrally as onesingle piece. Alternatively, portions of the atomizer may be separatelyformed and subsequently connected. As shown in FIGS. 2-9, rings (e.g.,202, 206) may be interconnected via peripherally positioned fins (e.g.,213, 214 and 215), which may be coupled to the periphery (e.g., outeredge) of the rings. Fins, in one example, include interconnectingportions (that may be formed of a metal) which force exhaust flow toproceed through other regions of the atomizer 200. Fins may be formedintegrally as a single unit in themselves, may be formed integrally withadjacent rings together as a single unit or may be individually formedand subsequently connected to other portions of the atomizer. If theatomizer is not formed integrally as a single unit, fins may be attachedto the rings by a variety of methods (e.g., welding).

In some embodiments, such as shown in FIG. 2 via atomizer 200, some orall of the fins are positioned annularly in a ring-shaped formation andangle inwards towards central axis 205 in a downstream direction andalso towards the smallest ring (e.g., fourth ring 228) in the atomizer200. Fins may be flat and angle inwards at an acute angle, or may havecurvature. Fins may also share a number of common attributes, includingthickness. As one non-limiting example, fin thickness may or may not beequivalent to ring thickness, or may vary among the pairs to which theyare attached.

The rings and fins together form annularly arranged apertures (e.g.,210), as shown, for instance, in FIG. 2. Apertures include hollowregions through which exhaust gas flows. In the example embodimentsprovided, some or all of the apertures (e.g., 210) are equally spacedannularly from one another, though unequal spacing may be possible aswell. As shown in FIGS. 2-9, apertures may include non-hollow regionsbetween rings and aperture bases, where aperture bases are portionscorresponding substantially to ring arcs and are perpendicular tocentral axis 205. Thus, the bases of apertures may not corresponddirectly to an outer edge of a ring, and some material (e.g., metal) maybe included between aperture bases and ring edges.

At least a portion of mixing region 130 in FIG. 1 comprises a ring(e.g., first ring 202) whose surface normal vector is parallel to theexhaust flow direction. As described above, the exhaust gas leaving theengine may first enter mixing region 130, wherein a fluid such as aliquid reductant (e.g., ammonia, urea, etc.) is injected into theexhaust system via the injector 136 as illustrated in FIG. 1. Rings(e.g., 202 and 206) along with fins (e.g., 213), in one example, may beconstructed of a type of metal, in which case they will be heated byexhaust flow. The liquid injection, which may be of various anglesincluding in-line with exhaust flow or oblique with respect to exhaustflow, in combination with the flow generated by the fins and apertures,guides exhaust flow around and through exhaust system atomizer 200.Further, vaporized liquid, which may be vaporized by the hot metal ofthe rings and fins, is drawn off exhaust system atomizer 200. Thus,exhaust system atomizer 200 aids in further mixing of the engine exhaustgas before the engine exhaust gas reaches SCR catalyst 140. In this way,by better mixing the engine exhaust gas, performance of SCR catalyst 140may be further enhanced, and thus, NOx may be further reduced.

In some embodiments, the fins of atomizer 200 may be considered asgeometrically complementary to their adjacent apertures, in which casemany of the fin properties discussed below imply consequent apertureproperties and vice versa. As seen, for example in FIG. 2, both theapertures (e.g., 210) and fins (e.g. 213) occupy annular regions definedby pairs of rings (e.g., the annular region between and defined by firstring 202 and second ring 206). In such an embodiment, both the aperturesand fins may be trapezoidal-shaped with curved bases. Other embodiments,however, are possible wherein fin and apertures may resemble alternativegeometries (e.g., rectangular, circular).

Fins (e.g., 213) have a first connecting region 220, defined by an arcof an upstream ring (e.g. an arc of first ring 202), and a secondconnecting region 222 defined by an arc of a downstream ring (e.g., anarc of second ring 206), both connecting regions shown in FIG. 2A. Inthis non-limiting example, the arc to which first connecting region 220corresponds is a portion of the outer edge of first ring 202. Likewise,the arc to which second connecting region 222 corresponds is a portionof the outer edge of second ring 206. Such arcs may be called connectionarcs, their lengths being designated connection arc lengths. Thisarrangement is seen in FIGS. 2 and 2A, while FIG. 3 shows that the finsmay be attached to the sidewalls of their respective rings. In otherembodiments, fins may also be coupled to the top or bottom edges of theadjacent upstream/downstream rings. With the exception of FIG. 8A, FIGS.2A, 3A, 4A, 5A, 6A, 7A and 9A show embodiments wherein the length ofsecond connecting region 222 is less than that of first connectingregion 220. The difference between the lengths may be constant for allfins in the atomizer 200, or may vary among the annular regions in theatomizer 200. Alternative embodiments may be possible in which thelength of second connecting region 222 of the fins is greater than thelength of first connecting region 220, as shown in FIG. 8A.

In one embodiment, the sides of fins are defined by line segmentspropagating from an upstream ring (e.g., first ring 202) to a downstreamring (e.g., second ring 206), the line segments being separated by anarc length 207, shown in FIG. 2A, concentric to all rings and centralaxis 205. An angle 209, also shown in FIG. 2A, sweeps out the arclength, wherein the angle 209 may be constant for all fins. The width ofthe fins, characterized by arc lengths whose endpoints correspond to themidpoints of the sides of the fins, may vary along the direction ofexhaust flow, forming a tapered shape as seen in FIGS. 2-9. It will beappreciated, however, that other embodiments are possible in which thesides of fins cannot be parameterized by rays extending from the centralaxis 205 to a fin base, or by line segments propagating from an upstreamring to a downstream ring. In other words, it is possible that fin sidesare not straight and do not project radially outward. Instead, in anon-limiting example, fin sides may be curved and may haveparabolically-shaped edges, for instance.

As shown at least at FIG. 2, fins (e.g., 213) connect first ring 202 tosecond ring 206, the rings together forming a first pair of rings 216. Afirst set of apertures 212 is included in this annular region, where thefirst set of apertures includes the aperture denoted by referencenumeral 212 and the other apertures in the annular region between anddefined by first ring 202 and second ring 206. In one embodiment, thefirst set of apertures 212 may comprise the same number of apertures asa second set of apertures 218, the second set of apertures 218 includingapertures in the annular region between and defined by second ring 206and third ring 208. Similarly, the number of fins provided among thefirst set of apertures 212 in its corresponding annular region may beequal to the number of fins provided among the second set of apertures218 in its corresponding annular region.

Fins (e.g., 213) in the annular region between and defined by first ring202 and second ring 206 form a first set of fins. Similarly, fins (e.g.,214) in the annular region between and defined by second ring 206 andthird ring 208 form a second set of fins. Still further, fins (e.g.,215) in the annular region between and defined by third ring 208 andfourth ring 228 form a third set of fins. In such an embodiment,alternating fins from the first and second sets of fins are connectedaround a periphery of a common ring (e.g., second ring 206).Geometrically, it may be that the first set of fins does not overlap thesecond set of fins. More specifically, in such a case no points in asecond connecting region (e.g., 222) of a fin in the first set of finsare shared with the points in a first connecting region (e.g., 220) of afin in the second set of fins. Alternatively phrased, no points in theshorter base of a fin in the first set of fins correspond to points inthe opposing base of a fin in the second set of fins. In this case, thefirst set of fins between a first pair of adjacent rings (e.g., 216) andthe second set of fins between a second pair of adjacent rings (e.g.,224) are angularly offset, the first and second pairs of rings sharingone common ring (e.g., second ring 206). Alternatively stated,connection arc lengths from the first and second sets of fins do notoverlap on the common ring (e.g., 206), the second set downstream fromthe first set. On the other hand, points in a first and/or secondconnecting region of a fin in the first set of fins may correspond topoints in a first and/or second connecting region of a fin in the thirdset of fins, the correspondence being that a ray extending from centralaxis 205 would intersect points in a first and/or second connectingregion of a fin in the third set of fins in addition to points in afirst and/or second connecting region of a fin in the first set of fins.This is shown in the face-on view of FIG. 2. Moreover, thecorrespondence may be such that a ray extending from central axis 205would intersect the midpoint of a first and/or second connecting regionof a fin in the third set of fins in addition to the midpoint of a firstand/or second connecting region of a fin in the first set of fins. Insuch a case the first set of fins and the third set of fins would besaid to be aligned.

The width of fins in a set of fins, compared to those in a set of finslocated upstream, may be less (e.g., the width of fins in the third setof fins may be less than the width of fins in the second set of fins, asshown in FIG. 2). More specifically, connection arc lengths coincidingwith a first and second connecting region may be longer for fins in thesecond set of fins than those for fins in the third set of fins. Thusconnection arc lengths on an upstream ring of the first pair of ringsmay differ from connection arc lengths on an upstream ring of the secondpair. Moreover, fin lengths may vary as the atomizer (e.g., 200) istraversed along the direction of exhaust flow. This may especially bethe case if the distances separating rings vary. Still further, fininclination, as measured by the angle between a first and secondconnecting region (e.g., 220 and 222 in FIG. 2A) may also vary. This mayespecially be the case if ring diameters are not reduced by a constantfactor as the atomizer is traversed along the direction of exhaust flow.In addition, fin geometry may be curved along the direction of exhaustflow. Alternatively, fins may be straight, minimizing length along thedirection of exhaust flow. However, certain commonalities may existamong the sets or entire plurality of fins, including tapered geometry,curved geometry towards central axis 205, material composition andthickness.

In some embodiments, second ring 206 and third ring 208 together form asecond pair of rings 224. First pair of rings 216 and second pair ofrings 224 share a common ring, namely second ring 206. Further, a fourthring 228 may be arranged downstream of third ring 208. Third ring 208and fourth ring 228 together form a third pair of rings 230. Second pairof rings 224 and third pair of rings 230 share a common ring, namelythird ring 208. In totality, such an embodiment comprises, among otherelements, exactly three pairs of rings, a total of four rings, threesets of apertures and fins, the rings being disposed concentricallyabout a central axis 205 and progressively downstream one another withdecreasing size in the direction of exhaust flow. FIGS. 2-4, 8 and 9represent this arrangement, though it will be understood that this ismerely an illustrative example and that different numbers of rings,fins, apertures and sets of apertures may be used without departing fromthe scope and spirit of the present disclosure.

Alternative embodiments including three rings, for example, are shown inFIGS. 5-7. In this example, an exhaust system atomizer 300 comprisesthree rings, two pairs of rings, three sets of apertures and fins, and aconvex disk 302. As in the embodiments shown in FIGS. 2-4, the length ofa second connecting region 222 of the fins is less than the length of afirst connecting region 220, creating a trapezoidal fin shape. Unlikethe embodiments heretofore disclosed, the convex disk 302 is positionedin a most upstream ring (e.g., third ring 208) and facing exhaust flow.The convex disk 302 has a curvature wherein a point coinciding with itscentral axis 205 is closer to a first ring 202 than points further awayfrom central axis 205. The convex disk 302 may be attached to third ring208 by a variety of methods (e.g., welding), or, as similarly disclosedabove, the exhaust system atomizer 300 may be integrally formed as oneunit. The convex disk 302 forces airflow to proceed through apertures210. In other words, no airflow may pass through third ring 208 but mayflow around it and through its apertures.

FIGS. 8 and 9 further illustrate alternative embodiments of exhaust gasatomizers in accordance with the present disclosure. FIG. 8. shows anatomizer 400 much like the atomizer 200 shown in FIGS. 2-4. In thisembodiment, however, FIG. 8A shows that the length of a first connectingregion 220 is less than the length of a second connecting region 222 forthe fins (e.g., 213) in atomizer 400, creating a trapezoidal fin shape.Conversely, FIG. 9A shows a portion of an atomizer 500 wherein lengthsof a first connecting region 220 are greater than the lengths of asecond connecting region 222 for the fins (e.g., 213). Moreover, FIG. 9shows that alternative dimensioning is possible. For example, ringthickness may be greater than the thicknesses shown in otherembodiments, and rings may be separated by a greater distance,increasing the fins' angle of inclination. Further, FIG. 9 shows thatunequal ring thickness may be possible. In this example, the thicknessof a fourth ring 508, as measured along the direction of exhaust flow,is greater than preceding rings 502, 504 and 506.

Thus, the claimed configuration allows for atomization to still beachieved, yet with a reduced impact to weight and cost. Exhaust systematomizer 200 may redirect a majority of the engine exhaust gas, whereasin some embodiments a minority of the engine exhaust gas may flowunobstructedly through the atomizer. This minority amount of the engineexhaust gas flowing unobstructedly may be offset by the cost and weightsavings achieved by the atomizer. Further, exhaust back pressure effectscan be reduced.

In this way, exhaust system 100 can achieve good atomization and mixing,while allowing for packaging space to be reduced. For example, incomparison to traditional exhaust systems, exhaust system 100 comprisingexhaust system atomizer 200 can facilitate parabolic flow, straightenthe flow pattern and maximize mixing efficiency. The fins increasesurface area, catching liquid droplets and allowing increased mixinginto turbulent exhaust flow.

It will be appreciated that the configurations and routines disclosedherein are exemplary in nature, and that these specific embodiments arenot to be considered in a limiting sense, because numerous variationsare possible. For example, the above technology can be applied to V-6,I-4, I-6, V-12, opposed 4, and other engine types. The subject matter ofthe present disclosure includes all novel and nonobvious combinationsand subcombinations of the various systems and configurations, and otherfeatures, functions, and/or properties disclosed herein.

The following claims particularly point out certain combinations andsubcombinations regarded as novel and nonobvious. These claims may referto “an” element or “a first” element or the equivalent thereof. Suchclaims should be understood to include incorporation of one or more suchelements, neither requiring nor excluding two or more such elements.Other combinations and subcombinations of the disclosed features,functions, elements, and/or properties may be claimed through amendmentof the present claims or through presentation of new claims in this or arelated application.

Such claims, whether broader, narrower, equal or different in scope tothe original claims, also are regarded as included within the subjectmatter of the present disclosure.

1. A system, comprising: an exhaust reductant injector upstream of amixer including: a plurality of concentrically smaller ringsinterconnected via fins having a width varying in a flow direction, thefins arranged annularly, and with a first set of fins between a firstpair of adjacent rings angularly offset from a second set of finsbetween a second pair of adjacent rings, the first and second pairs ofrings sharing one common ring.
 2. The system of claim 1 wherein theplurality of concentrically smaller rings includes three or more pairsof adjacent rings.
 3. The system of claim 1 wherein alternating finsfrom the first and second sets are connected around a periphery of thecommon ring.
 4. The system of claim 1 wherein the fins angle inwardtoward a central axis of an exhaust pipe in which the mixer ispositioned, where the central axis of concentric rings share a centralaxis of the exhaust pipe.
 5. The system of claim 1 wherein connectionarc lengths on an upstream ring of the first pair differ from connectionarc lengths on an upstream ring of the second pair.
 6. The system ofclaim 1 wherein connection arc lengths from the first and second sets offins do not overlap on the common ring, the second set downstream fromthe first set.
 7. The system of claim 1 wherein each fin has a firstconnecting region defined by an arc of an upstream ring, a secondconnecting region defined by an arc of a downstream ring, each fin alsohaving a common thickness.
 8. The system of claim 1 wherein a number offins in the first set is equal to a number of fins in the second set. 9.The system of claim 1 further comprising a convex disk facing exhaustflow positioned in a most upstream ring.
 10. The system of claim 1wherein an SCR catalyst is positioned downstream of the mixer.
 11. Asystem, comprising: an exhaust reductant injector upstream of a mixerincluding: a plurality of concentrically smaller rings interconnectedvia fins arranged annularly, and with a first set of fins between afirst pair of adjacent rings angularly offset from a second set of finsbetween a second pair of adjacent rings, the first and second pairs ofrings sharing one common ring, with alternating fins from the first andsecond sets connected around a periphery of the common ring.
 12. Thesystem of claim 11 wherein the plurality of concentrically smaller ringsincludes three or more pairs of adjacent rings.
 13. The system of claim11 wherein all of the fins angle inward toward a central axis of anexhaust pipe in which the mixer is positioned, where the central axis ofconcentric rings share a central axis of the exhaust pipe.
 14. Thesystem of claim 13 wherein connection arc lengths on an upstream ring ofthe first pair differ from connection arc lengths on an upstream ring ofthe second pair.
 15. The system of claim 14 wherein connection arclengths from the first and second sets of fins do not overlap on thecommon ring, the second set downstream from the first set.
 16. Thesystem of claim 13 wherein a number of fins in the first set is equal toa number of fins in the second set, and an SCR catalyst is positioneddownstream of the mixer.
 17. A system, comprising: an exhaust pipe; anangled exhaust injector positioned in a wall of the exhaust pipe; an SCRcatalyst coupled in the exhaust pipe; and a mixer positioned internallyto the exhaust pipe downstream of the injector and upstream of the SCRcatalyst, the mixer including a telescope-shaped set of rings, withprogressively smaller rings positioned downstream one another, adjacentrings connected via peripherally positioned flat angled fins.
 18. Thesystem of claim 17 wherein the exhaust pipe is coupled to an exhaust ofa diesel engine, and wherein ring sets are coupled to one another viathe fins.
 19. The system of claim 18 wherein each set of rings iscoupled with a same number of fins.
 20. The system of claim 18 wherein acentral axis of each ring aligns with a central axis of the exhaustpipe.